Yb 3+ ‐Complex‐Mediated Assembly of CsPbBr 3 Nanocrystals Enables Multilevel Optical Encryption

Abstract Counterfeiting presents severe global economic and safety threats, driving demand for advanced anti‐counterfeiting solutions. While CsPbBr 3 perovskite nanocrystals (NCs) offer exceptional optical encoding properties, their application is limited by intrinsic instability and single‐mode emission. This work introduces a tripodal quaternary ammonium‐functionalized Yb 3+ complex ([YbL 3 ] 3+ ) as a “molecular adhesive” to simultaneously address these constraints. The complex directs CsPbBr 3 NC self‐assembly into ordered 3D cubic superstructures (Yb‐CsPbBr 3 SNCs) via ionic interactions while passivating surface defects. Resultant Yb‐CsPbBr 3 SNCs exhibit three critical advances: 1) Dual‐mode luminescence (519 nm NC green emission; 980 nm Yb 3+ NIR emission) enabling covert authentication; 2) Significantly enhanced environmental stability, particularly against water and heat; 3) Intrinsic microscale assembly randomness permitting physically unclonable function (PUFs) generation for high‐security encryption. Exploiting differential NIR emission, thermal stability, and humidity sensitivity between Yb‐CsPbBr 3 SNCs and CsPbBr 3 NC, a multi‐stimuli‐responsive (NIR/thermal/humidity) anti‐counterfeiting platform is demonstrated with flexible “one‐time” or “repeated” decryption. Stochastic assembly further enables high‐capacity PUFs exhibiting validated randomness, uniqueness, and similarity index. This Yb 3+ ‐complex‐mediated assembly strategy overcomes perovskite NC stability and encoding limitations, unlocking dual‐mode luminescence and unclonable security features to establish a versatile platform for next‐generation anti‐counterfeiting and optical encryption.